Stabilized polyether polyol and polyurethane foam obtained therefrom

ABSTRACT

A stabilizer composition useful as an additive for polyether polyols, particularly those employed in the manufacture of polyurethane foams, is provided which comprises a diarylamine, a sterically hindered phenol and a pentaerythritol diphosphite.

BACKGROUND OF THE INVENTION

This invention relates to a stabilizer composition, to a polyetherpolyol stabilized against degradation by the stabilizer composition andto a polyurethane foam obtained from the stabilized polyether polyol.

U.S. Pat. No. 3,280,049 discloses a stabilizer composition consisting ofa sterically hindered phenol.

U.S. Pat. Nos. 3,567,664, 3,637,865, 4,010,211, 4,021,385, 4,070,304,4,265,783 and 4,275,173 disclose stabilizer compositions consisting ofmixtures of sterically hindered phenols with substituted diphenylamines.

U.S. Pat. No. 3,969,315 discloses a stabilizer composition consisting ofa mixture of an alkyl phenyl propylene glycol phosphite and either ahindered phenol or an amine.

U.S. Pat. No. 4,794,126 discloses a stabilizer composition consisting ofa mixture of a diaryl arylenediamine, a sterically hindered phenol andthe reaction product of a diarylamine with a lower alkyl ketone.

U.S. Pat. No. 4,933,374 discloses a stabilizer composition derived froma mixture of 2,6-di-tert-butyl-4-sec-butylphenol and the reactionproduct of diisobutylene, styrene and diphenylamine and, optionally,trihydrocarbyl phosphite as color stabilizer.

U.S. Pat. No. 5,077,321 discloses a stabilizer composition consisting ofa mixture of at least two compounds selected from a thiophenol, adiphenyl sulfide and a diphenylamine.

The use of various phosphites in stabilizer compositions is discussed inCapolupo et al., "The History and Trends of Phosphites in the PlasticsIndustry," in History of Polymeric Composites: Invited Papers Presentedat the American Chemical Society Symposium on the Origin & Developmentof Polymeric Composites, Anaheim, Calif., September, 1986, ed. by R. B.Seymour & R. D. Deanin (1987). Tris(nonylphenyl)phosphite, distearylpentaerythritol diphosphite, bis(2,4-di-t-butylphenyl)pentaerythritoldiphosphite, and tris(2,3-di-t-butylphenyl)phosphite are disclosed,inter alia, as antioxidants useful in the manufacture of variousplastics.

SUMMARY OF THE INVENTION

In accordance with the present invention, a stabilizer composition isprovided which comprises:

a) a diarylamine;

b) a sterically hindered phenol; and,

c) a pentaerythritol diphosphite.

The foregoing stabilizer composition is especially useful as an additivefor polyether polyols, particularly those employed in the manufacture ofpolyurethane foams where it further serves to prevent or reducediscoloration and scorching of the foamed products. This inventionprovides the following advantages over those currently in use:

a) reduced handling;

b) increased hydrolytic stability as compared to other liquid phosphitescontaining stabilizer systems;

c) reduced processing time due to elimination of filtration step;

d) increased color stability of stabilizer composition due to additionof phosphite.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The diarylamines, hindered phenols and pentaerythritol diphosphites thatare employed in the stabilizer composition of this invention areindividually well known compounds.

Suitable diarylamines that can be employed in the liquid stabilizercomposition herein include diphenylamine,p,p'-di-tert-octyldiphenylamine, p,p'-di-α-phenylethyldiphenylamine,p-tert-octyl-p'-phenylethyl-diphenylamine, p-tert-octyldiphenylamine,p-phenylethyldiphenylamine, tri-t-octyldiphenylamine,p-tert-butyldiphenylamine, p,p'-di-tert-butyldiphenylamine,p-tert-octyl-p'-butyldiphenylamine,p-tert-butyl-p'-phenylethyldiphenylamine, phenyl-betadiphenylamine, theditolylamines, the phenyltolylamines, the dinaphthylamines,dianilinodiphenylmethane, p-hydroxyldiphenylamine,p-amino-diphenylamine, N,N'-diphenyl-p-phenylenediamine,p-chlorodiphenylamine, p-isopropoxydiphenylamine and the like. A mixtureof alkylated diphenylamines comprising butylated and octylated speciescan be obtained by reacting isobutylene with diphenylamine. Thismixture, which is preferred, is commercially available under thetradename Naugard PS-30 (Uniroyal Chemical Co.).

The diarylamine component of the stabilizer composition of thisinvention can be present therein in widely varying amounts, e.g., fromabout 10 to about 90, preferably from about 20 to about 60, and mostpreferably from about 30 to about 50, weight percent based on the entireweight of stabilizer composition.

Suitable hindered phenols that can be utilized in the liquid stabilizercomposition herein include 2,4-dimethyl-6-octylphenol,2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-nonylphenol,2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-n-butylphenol,2,6-di-t-butyl-4-sec-butylphenol,2,2'-methylenebis(4-methyl-6-t-butylphenol),2,2'-methylenebis(4-ethyl-6-t-butylphenol),2,4-dimethyl-6-t-butylphenol, 4-hydroxymethyl-2,6-di-t-butylphenol,n-octadecyl-β(3,5 di-t-butyl-4-hydroxyphenyl)propionate,4,4'-dihydroxydiphenol, 4,4'-thiobis(6-t-butyl-o-cresol), p-butylphenol,p-isopropylphenol, p-(1,1,3,3-tetramethylbutyl)phenol, thymol, mixed m-and p-cresol, p-nonylphenol, other phenols, cresols having alkylsubstituents and mixtures thereof. A preferred hindered phenol is2,6-di-t-butyl-4-sec-butylphenol, which is commercially available underthe tradenames Isonox 132 (Schenectady Chemical Co.) and Vanox 1320 (R.T. Vanderbilt Co.).

The hindered phenol component of the stabilizer composition of thisinvention can be present therein in widely varying amounts, e.g., fromabout 10 to about 90, preferably from about 40 to about 80, and mostpreferably from about 50 to about 70, weight percent based on the entireweight of stabilizer composition.

The pentaerythritol diphosphites that can be utilized in the stabilizercomposition herein are preferably the sterically hinderedbis(aryl)pentaery-thritol diphosphites, numerous examples of which areknown in the art, e.g., as disclosed in U.S. Pat. Nos. 2,847,443,4,302,383, 4,305,866 and 4,692,539. Of these preferred diphosphites,those in which the aryl groups are substituted with branched alkylgroups of from about 3 to about 30 carbon atoms are particularlypreferred. The aryl groups are preferably phenyl groups and containbranched alkyl groups in the 2 and 4 positions relative to one anotheron the phenyl ring. An especially preferred pentaerythritol diphosphitefor use herein is bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite(referred to herein as BPD), which is available under the tradenameUltranox 626 (General Electric Specialty Chemicals). This compoundcontains approximately 1 weight percent of triisopropanolamine to addhydrolytic stability to the diphosphite.

BPD is a high performance solid organophosphate antioxidant which isknown for its stabilization of polyolefins, polyesters, styrenes,engineering thermoplastics, polyvinyl chlorides, elastomers andadhesives. BPD is known to exhibit superior stability compared to otherphosphite compositions currently employed in the manufacture ofpolyurethane foams and other polymeric materials. Examples of suchcurrently employed phosphites are tris (nonylphenyl) phosphite, phenyldiisodecyl phosphite, tris(2,4-di-t-butylphenyl)phosphite, tridecylphosphite and triisooctyl phosphite.

Of the three components of the stabilizer composition herein, thepentaerythritol diphosphite component will generally be present in thelowest amount, e.g., from about 0.1 to about 10, preferably from about 1to about 8, and most preferably from about 3 to about 5, weight percentbased on the entire weight of stabilizer composition.

As previously indicated, the stabilizer composition of this invention isparticularly useful for the stabilization of polyether polyols,primarily from degradation resulting from oxidation. The polyetherpolyols are well known in the art and are obtained by reactingpolyhydric alcohols, e.g., those containing from 2-8 hydroxyl groupssuch as ethylene glycol, propylene glycol, diethylene glycol,2,3-butylene glycol, 1,3-butylene glycol, 1,5-pentane diol, glycerol,trimethylolpropane, triethylolpropane, sorbitol, pentaerythritol, andmixtures thereof, with a 1,2-epoxide, e.g., ethylene oxide, propyleneoxide, butylene oxide, cyclohexane oxide, glycidol and the halogenatedalkylene oxides such as 4,4,4-trichloro-1,2-epoxybutane, and mixturesthereof. The preferred polyether polyols contain from 2-4 hydroxylgroups and are obtained by reacting one or more polyhydric alcoholshaving a like number of hydroxyl groups with ethylene oxide, propyleneoxide, butylene oxide, and mixtures thereof.

The stabilizer composition is added to the polyether polyol in an amountsufficient to impart an appreciable stabilizing effect. In general, thisamount may vary from about 0.1 to about 2 weight percent, preferablyfrom about 0.2 to about 1 weight percent and most preferably from about0.4 to about 0.6 weight percent by total weight of polyether polyol(s).Where the polyether polyol is to be employed in the manufacture of apolyurethane foam and stabilization of the polyol is not in issue, thestabilizer composition may be added to some other component of thepolyurethane-forming reaction mixture, e.g., to the polyisocyanate,prepolymer, foaming agent, etc., or to the reaction mixture once formed,rather than to the polyol. In this case, the foregoing amounts ofstabilizer composition calculated on the basis of the total polyetherpolyol component can be utilized.

Any suitable organic isocyanate which is capable of reacting with apolyether polyol to form a polyurethane can be employed in preparing thefoam. This includes diisocyanates and polyisocyanates, e.g.,triisocyanates and polymeric isocyanates. Due to their commercialavailability, the polymeric isocyanates and tolylene diisocyanate arepreferred. The latter, the use of which is more preferred, can besupplied in the form of an isomeric mixture of about 80 weight percentof 2,4-isomer and about 20 weight percent of 2,6-isomer. Other typicalisocyanates include 4,4'-methylene-bis(phenylisocyanate),3,3'-bitolylene-4,4'-diisocyanate,3,3'-dimethoxy-biphenylene-4,4'-diisocyanate,naphthalene-1,5-diisocyanate, hexamethylene diisocyanate, 1,4-phenylenediisocyanate, polyphenylene polymethylene isocyanate, etc. The amount ofisocyanate employed in the preparation of the polyurethane foams shouldbe sufficient to provide at least about 0.7 NCO groups per hydroxylgroup present in the reaction system. An excess of isocyanate compoundcan be conveniently employed; however, the use of a large excess isgenerally undesirable due to the high cost of the isocyanate compounds.It is preferable, therefore, to employ no greater than about 1.5 NCOgroups per hydroxyl group, and still more preferably from about 0.9 toabout 1.3 NCO groups per hydroxyl group.

In preparing the polyurethane foams, the polyether polyol is reactedwith the organic isocyanate in the presence of a foaming agent and areaction catalyst. The foaming agent can be any one of those known to beuseful for this purpose, such as water, which is preferred, thehalogenated hydrocarbons and mixtures thereof. Typical halogenatedhydrocarbons include monofluorotrichloromethane,difluorodichloromethane, 1,1,2-trichloro-1,2,2-trifluoroethane,methylene chloride, etc. The amount of foaming agent employed can bevaried within a wide range. Generally, however, the halogenatedhydrocarbons are employed in an amount from about 1 to about 50 parts byweight per 100 parts by weight of the polyether polyol, and generallywater is employed in an amount of from about 0.1 to about 10 parts byweight per 100 parts by weight of the polyether polyol.

The catalyst used in preparing the polyurethane foams can be any one ofthose known to be useful for this purpose or mixtures thereof, includingtertiary amines and metallic salts. Typical tertiary amines includeN-methyl morpholine, N-hydroxyethyl morpholine, triethylene diamine,dimethyl ethanolamine, tetramethylbutane diamine, trimethylamine,triethylamine, etc. Typical metallic salts include the salts ofantimony, tin and iron, e.g., dibutyltin dilaurate, stannous octoate,etc. Generally speaking, the catalyst is employed in an amount rangingfrom about 0.1 to about 2.0 weight percent based on the weight of thepolyether polyol.

It is preferred in the preparation of the polyurethane foams of thepresent invention to employ minor amounts of a surfactant in order toimprove the cell structure of the polyurethane foams. Typical of suchsurfactants are the silicon-based surfactants as disclosed, e.g., inU.S. Pat. No. 2,834,748 and in the book "Rigid Plastic Foams" by T. H.Ferrigno (1963), Reinhold Publishing Company. Other suitable compoundsuseful as surfactants include synthetic detergents such as oxyethylatednonyl phenol and other ethylene oxide and glycidol-based surfactants.Generally up to about 2 parts by weight of the surfactant is employedper 100 parts by weight of polyether polyol.

Various additives can also be employed in preparing the foam which serveto provide different properties. Fillers, e.g., clay, calcium sulfate,barium sulfate, ammonium phosphate, etc., can be added to lower cost andimprove physical properties. Dyes can be added for color and fibrousglass, asbestos, or synthetic fibers can be added for strength. Inaddition, plasticizer, deodorants and flame retardants can be added.

The following examples are illustrative of the invention.

EXAMPLE 1

This example illustrates the preparation of a stabilizer composition inaccordance with the invention.

2,6-di-t-butyl 4-sec-butylphenol (1,914 g; Isonox 132), a mixture ofbutylated and octylated diphenylamines (1,254 g; Naugard PS-30) andbis(2,4-di-t-butylphenyl)pentaerythritol diphosphite (BPD) (132 g;Ultranox 626) were placed in a 5-liter glass beaker and mixed using a3-inch stirring bar on a magnetic stirring hot plate. The beaker wascovered with aluminum foil to minimize oxidation. Inert nitrogen wasbubbled into the mixture which was then heated to 90° C. over a 30minute period. The mixture was heated at 90° C. for 2 hours.

In subsequent batches, BPD was stirred into the 2,6-di-t-butyl4-sec-butylphenol and the butylated and octylated diphenylamine mixturewas thereafter added. The composition was thereafter hand-mixed with aspatula and allowed to stand for approximately 1 hour prior to heating.The mixture became a clear solution at about 80° C.

EXAMPLE 2

In three separate trials, three polyurethane foam-forming reactionmixtures (A through C) were prepared using the materials listed in TableI below. Each reaction mixture employed a 3000 g/mol. average molecularweight polyether polyol, i.e., Polyol 16-52 (AC West Virginia), whichhad been minimally stabilized against oxidative degradation with 100 ppmbutylated hydroxy toluene. The three reaction mixtures differprincipally in the amount of foaming agent, i.e., water, and toluene.diisocyanate present therein.

                  TABLE I    ______________________________________    POLYURETHANE FOAM-FORMING    REACTION MIXTURES                  Reaction Mixture                  A       B       C    ______________________________________    Polyol 16-52 (g)                    200       200     200    Water (parts by weight                    8.0       10.0    11.0    of polyol)    Niax A-1 Amine  0.06      0.06    0.14    Catalyst (g)    L-620 Surfactant (g)                    2.0       2.0     2.4    FR Thermolin 101 (g)                    14.0      14.0    14.0    T-9 Tin Catalyst (g)                    0.36      0.46    0.50    Toluene diisocyanate (g)                    108.9     131.2   142.3    (80:20 isomer mixture)    Isocyanate Index                    115       115     115    ______________________________________

To prepare each of the foregoing reaction mixtures, a premix containingwater, Niax A-1 amine catalyst (Union Carbide Co.) and L-620 siliconesurfactant (Union Carbide Co.) was added to a mixture containing 200 gof the polyether polyol, FR Thermolin 101 as fire retardant (Olin Corp.)and one of the five stabilizer compositions of Table II set forth below.

                  TABLE II    ______________________________________    STABILIZER COMPOSITIONS                    Stabilizer Composition (SC)                    SC-1 SC-2   SC-3   SC-4 SC-5    ______________________________________    Naugard 445,      1900   2000    4,4'-di(α,α-dimethyl-    benzyl) diphenylamine, ppm    Butylated hydroxytoluene,                      2600   3000    hindered phenol, ppm    Naugard PS-30 ppm               1900 1900 1800    Isonox 132 2,6-di-t-butyl-4-    2900 2900 2800    sec-butylphenol, ppm    Ultranox 626                          200  400    bis(2,4-di-t-butylphenyl)    pentaerythritol diphosphite, ppm    Naugard R, paraphenylene         200    diamine, ppm    ______________________________________

The FR Thermolin 101 was added to the polyol prior to adding otherformulation ingredients. T-9 tin catalyst (Air Products Corp.) was thenadded to the composition and mixed in a high speed lightning mixer for 5seconds. The final ingredient, toluene diisocyanate (a 20:80 weightpercent mixture of the 2,4-isomer and 2,6 isomer supplied by MobayCorp.), was thereafter added. The mixture was stirred at high speed for7 additional seconds and then poured into a 10"×10"×5" cardboardcontainer. The foam was allowed to rise completely at room temperatureand then allowed to stand for 5 additional minutes.

Stabilizer Compositions 1 (SC-1), 2 (SC-2) and 3(SC-3) represent knownstabilizer compositions. Stabilizer Compositions 4 (SC-4) and 5 (SC-5)represent stabilizer compositions in accordance with the presentinvention.

In this manner, 15 samples of polyurethane foam were obtained forevaluation, i.e., the Reaction Mixtures A, B and C of Table I containingeach of the five Stabilizer Compositions SC-1 to SC-5 of Table II.

EXAMPLE 3

Scorch resistance of the 15 polyurethane foams of Example 2 wasdetermined by the microwave scorch test in the following manner: thesides of the cardboard container were removed and the foam specimen wascured in a microwave oven for 17.5 minutes at the 20 percent powersetting. The foam was then air cured in an air circulating oven for 3minutes at 125° C. immediately after the microwave curing step. Afterremoval from the air circulating oven, the foam was cut in halfhorizontally to the rise of the foam and analyzed for degree of scorchand color using the HunterLab Colorimeter Model D25M/L. A numericalvalue was assigned to the color of each foam sample. Three colorcharacteristics, i.e., redness/greenness (a), yellowness/blueness (b)and lightness (L), of the foam were measured and compared to a whitetile standard. Using these values, Hunter Color ΔE, or total colordifference, was calculated according to the following equation:

    ΔE=(ΔL.sup.2 +Δa.sup.2 +Δb.sup.2).sup.1/2

Table III below sets forth the Hunter Color ΔE and (b) values for foamsprepared using the various stabilizer systems described in detail above.

                  TABLE III    ______________________________________    MICROWAVE SCORCH TEST DATA    Stabilizer  Reaction Mixture    Composition A            B      C    ______________________________________              Hunter Color ΔE values    SC-1        43           33     31    SC-2        38           33     30    SC-3        37           38     34    SC-3        34           39     35    SC-5        43           36     39              Hunter Color (b) values    SC-1        23.3         24.6   23.8    SC-2        23.6         24.1   22.5    SC-3        23.2         23.0   23.5    SC-4        21.5         24.0   24.0    SC-5        23.1         23.0   23.5    ______________________________________

The above results demonstrate that for Reaction Mixture A, StabilizerComposition 4 provided the highest degree of scorch protection whencomparing the Hunter Color ΔE and (b) values of the various StabilizerCompositions.

EXAMPLE 4

The data for the degree of scorch protection provided by the stabilizercompositions were obtained by visual measurement, the results being setforth in Table IV below. The scorch protection afforded by each of thestabilizer compositions was scaled from 1 to 10 with 1 being the best,and 10 being the worst, degree of scorch protection.

                  TABLE IV    ______________________________________    MICROWAVE SCORCH TESTING OF    POLYURETHANE FOAM    (INDUSTRY SCALE 1-10)    Stabilizer   Reaction Mixture    Composition  A            B     C    ______________________________________    SC-1         3.2          3.0   2.2    SC-2         3.0          2.2   2.0    SC-3         3.0          3.0   2.1    SC-4         2.1          3.0   2.1    SC-5         3.2          2.2   3.0    ______________________________________

These results clearly indicate that SC-4 provides greater scorchprotection relative to the known stabilizer compositions, i.e., SC-1,SC-2 and SC-3, for the foams produced from Reaction Mixture A. In thefoams produced from Reaction Mixture B, SC-5 provided the greatestdegree of scorch protection and SC-4 performed at least as effectivelyas the known stabilizer compositions SC-1 and SC-3. In the foamsproduced from Reaction Mixture C, SC-4 performed comparably to the knownstabilizer compositions.

EXAMPLES 5-6 AND COMPARATIVE EXAMPLES 1-6

To determine the effect of phosphites on the performance of polyolstabilizer compositions, various phosphites were mixed with butylatedhydroxy toluene and styrenated diphenylamine and tested as stabilizercompositions for polyether polyols. Polyurethane foams manufactured inpart from the polyether polyols stabilized with thesephosphite-containing stabilizer compositions were subjected to themicrowave scorch test as discussed in Example 3 and examined for degreeof scorch.

The polyether polyol possessed an average molecular weight of 3000 g/moland was minimally stabilized with 100 ppm butylated hydroxy toluene (DowVoranol 3137). Eight 200 gram samples of the polyether polyol wereindividually stabilized with the antioxidant compositions presented inTable V below. Examples 5 and 6 represent the stabilizer composition ofthis invention. Comparative Example 1 contains no phosphite andComparative Examples 2-6 contain standard phosphites. The stabilizedpolyol was added to a premix containing water (100 g), A-1 catalyst(0.20 g; Union Carbide) and L-5810 silicone surfactant (2.0 g; UnionCarbide). The mixture was stirred in a lightning mixer for 5 seconds athigh speed. T-10 catalyst (0.40 g; a mixture of stannous octoate anddioctyl phthalate from Air Products Corp.) was then added and theresulting mixture was stirred for 5 seconds in the lightning mixer.Toluene diisocyanate (126.0 g; an 80:20 weight percent mixture of the2,6-isomer and 2,4-isomer supplied by Mobay Corp.) was added and themixture was again stirred at high speed for 7 additional seconds. Themixture was thereafter poured into a 10"×10"×5" cardboard container andthe resulting foam was allowed to rise completely.

After the foam rose completely at room temperature, it was allowed tostand for 5 additional minutes. The sides of the cardboard containerwere then removed and the sample was cured in a microwave oven for 5minutes and 38 seconds at 50 percent power. Immediately thereafter, thesample was oven cured for 3 minutes at 125° C.

The specimens were cut in half, horizontally to the rise of the foam,and analyzed for degree of scorch. The performance ratings are based ona scale of 1-10 with 1 representing the best scorch protection and 10being the worst. The data are presented in Table V below:

                                      TABLE V    __________________________________________________________________________    SCORCH PROTECTION PROVIDED BY PHOSPHITE-CONTAINING    STABILIZER COMPOSITIONS                         Ultranox 626           Naugard                 Wingstay 29                         (ppm) (bis(2,4-                                  Wytox 312                                         Weston           BHT (ppm)                 (ppm)   di-t-butylphenyl)                                  (ppm) (tris                                         TDP (ppm)           (hindered                 (styrenated                         pentaerythritol                                  (nonylphenyl)                                         (tridecyl    Example           phenol)                 diphenylamine)                         diphosphite)                                  di-phosphite)                                         phosphite)                                               Performance    __________________________________________________________________________    5      4000  900     100      --     --    1-2    6      4000  800     200      --     --    1    Comp. Ex. 1           4000  1000    --       --     --    2    Comp. Ex. 2           4000  900     --       100    --    2    Comp. Ex. 3           4000  900     --       --     100   1-2    Comp. Ex. 4           4000  800     --       200    --    2    Comp. Ex. 5           4000  800     --       --     200   1-2    Comp. Ex. 6           4000  1000    --       --     200   1-2    __________________________________________________________________________

The above data show that the stabilizer composition containing thepentaerythritol diphosphite (Examples 5 and 6) performed as good as orbetter than the stabilizer compositions of the Comparative Examples 1-6.

What is claimed is:
 1. A liquid stabilizer composition comprising:a) adiarylamine; b) a hindered phenol; and, c) a pentaerythritoldisphosphite.
 2. The liquid stabilizer composition of claim 1 whereinthe diarylamine is present at a level of from about 10 to about 90weight percent, the hindered phenol is present at a level of from about10 to about 90 weight percent and the pentaerythritol diphosphite ispresent at a level of from about 0.1 to about 10 weight percent.
 3. Theliquid stabilizer composition of claim 1 wherein the diarylamine ispresent at a level of from about 20 to about 60 weight percent, thehindered phenol is present at a level of from about 40 to about 80weight percent and the pentaerythritol diphosphite is present at a levelof from about 1 to about 8 weight percent.
 4. The liquid stabilizercomposition of claim 1 wherein the diarylamine is selected from thegroup consisting of diphenylamine, p,p'-di-tert-octyldiphenylamine,p,p'-di-α-phenylethyldiphenylamine,p-tert-octyl-p'-phenylethyl-diphenylamine, p-tert-octyldiphenylamine,p-phenylethyldiphenylamine, tri-t-octyldiphenylamine,p-tert-butyldiphenylamine, p,p'-di-tert-butyldiphenylamine,p-tert-octyl-p'-butyldiphenylamine,p-tert-butyl-p'-phenylethyldiphenylamine, phenyl-betadiphenylamine, theditolylamines, the phenyltolylamines, the dinaphthylamines,dianilinodiphenyl-methane, p-hydroxyldiphenylamine,p-amino-diphenylamine, N,N'-diphenyl-p-phenylenediamine,p-chlorodiphenylamine, p-isopropoxydiphenylamine and mixtures thereof.5. The liquid stabilizer composition of claim 1 wherein the hinderedphenol is selected from the group consisting of2,4-dimethyl-6-octylphenol, 2,6-di-t-butyl-4-methylphenol,2,6-di-t-butyl-4-nonylphenol, 2,6-di-t-butyl-4-n-butylphenol,2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-sec-butylphenol,2,2'-methylenebis(4-methyl-6-t-butylphenol),2,2'-methylenebis(4-ethyl-6-t-butylphenol),2,4-dimethyl-6-t-butylphenol, 4-hydroxymethyl-2,6-di-t-butylphenol,n-octadecyl-β(3,5 di-t-butyl-4-hydroxyphenyl) propionate,4,4'-dihydroxydiphenol, 4,4'-thiobis(6-t-butyl-o-cresol), p-butylphenol,p-isopropylphenol, p-(1,1,3,3-tetramethylbutyl)phenol, thymol, mixed m-and p-cresol, p-nonylphenol and mixtures thereof.
 6. The liquidstabilizer composition of claim 1 wherein the pentaerythritoldiphosphite is a bis(aryl) pentaerythritol diphosphite.
 7. The liquidstabilizer composition of claim 6 wherein the aryl group is a phenylgroup containing at least 2 branched alkyl groups of from about 3 toabout 30 carbon atoms.
 8. The liquid stabilizer composition of claim 1wherein the pentaerythritol diphosphite isbis(2,4-di-t-butylphenyl)pentaerythritol diphosphite.
 9. The liquidstabilizer of claim 1 wherein the diarylamine is selected from the groupconsisting of diphenylamine, p,p'-di-tert-octyldiphenylamine,p,p'-di-α-phenylethyldiphenylamine,p-tert-octyl-p'-phenylethyl-diphenylamine, p-tert-octyldiphenylamine,p-phenylethyldiphenylamine, tri-t-octyldiphenylamine,p-tert-butyldiphenylamine, p,p'-di-tert-butyldiphenylamine,p-tert-octyl-p'-butyldiphenylamine,p-tert-butyl-p'-phenylethyldiphenylamine, phenyl-betadiphenylamine, theditolylamines, the phenyltolylamines, the dinaphthylamines,dianilinodiphenylmethane, p-hydroxyldiphenylamine,p-amino-diphenylamine, N,N'-diphenyl-p-phenylenediamine,p-chlorodiphenylamine, p-isopropoxydiphenylamine, and mixtures thereof,the hindered phenol is selected from the group consisting of2,4-dimethyl-6-octylphenol, 2,6-di-t-butyl-4-methylphenol,2,6-di-t-butyl-4-nonylphenol, 2,6-di-t-butyl-4-n-butylphenol,2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-sec-butylphenol,2,2'-methylenebis(4-methyl-6-t-butylphenol),2,2'-methylenebis(4-ethyl-6-t-butylphenol),2,4-dimethyl-6-t-butylphenol, 4-hydroxymethyl-2,6-di-t-butylphenol,n-octadecyl-β(3,5 di-t-butyl-4-hydroxyphenyl)propionate,4,4'-dihydroxydiphenol, 4,4'-thiobis(6-t-butyl-o-cresol), p-butylphenol,p-isopropylphenol, p-(1,1,3,3-tetramethylbutyl)phenol, thymol, mixed m-and p-cresol, p-nonylphenol, and mixtures thereof and thepentaerythritol diphosphite is a bis(aryl)pentaerythritol diphosphite.10. The liquid stabilizer composition of claim 9 wherein the aryl groupis a phenyl group containing at least two branched alkyl groups of from3 to about 30 carbon atoms.
 11. The liquid stabilizer composition ofclaim 9 wherein the bis(aryl)pentaerythritol diphosphite isbis(2,4-di-t-butylphenyl)pentaerythritol diphosphite.
 12. The liquidstabilizer composition of claim 9 wherein the diarylamine is present ata level of from about 10 to about 90 weight percent, the hindered phenolis present at a level of from about 10 to about 90 weight percent andthe pentaerythritol diphosphite is present at a level of from about 0.1to about 10 weight percent.
 13. The liquid stabilizer composition ofclaim 9 wherein the diarylamine is present at a level of from about 20to about 60 weight percent, the hindered phenol is present at a level offrom about 40 to about 80 weight percent and the pentaerythritoldiphosphite is present at a level of from about 1 to about 8 weightpercent.
 14. The liquid stabilizer composition of claim 9 wherein thediarylamine is a mixture of butylated diphenylamine and octylateddiphenylamine present at a level of from about 20 to about 60 weightpercent, the hindered phenol is 2,6-di-t-butyl-4-sec-butylphenol presentat a level of from about 40 to about 80 weight percent and thepentaerythritol diphosphite is bis(2,4-di-t-butylphenyl) pentaerythritoldiphosphite present at a level of from about 1 to about 8 weightpercent.